An illuminating optical system is realized which can efficiently produce longer-life and higher-luminance illuminating light with a small etendue. The illuminating optical system includes a concave reflection mirror (100), a fluorescent material supporting body (400) that supports fluorescent materials (401 to 403) at the substantially the focal point position of the concave reflection mirror, a plurality of laser light sources (200) that are disposed on the concave reflection mirror at positions perpendicular to the central axis of the concave reflection mirror and that emit excitation light toward the fluorescent materials, and a window (102) covering the open surface of the concave reflection mirror that reflects the excitation light and allows to pass therethrough fluorescence generated when the fluorescent material is irradiated with the excitation light.
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